This application is based on and claims the priority under 35 U.S.C. xc2xa7119 of German Patent Application 101 47 827.5, filed on Sep. 27, 2001, the entire disclosure of which is incorporated herein by reference.
The invention relates to a flap arrangement that can be selectively extended to protrude into an airflow boundary layer of an aerodynamic element, such as a wing, an aileron, a rudder, an elevator, a stabilizer surface, or a flap, preferably having a planar trailing edge, so as to selectively vary the aerodynamic lift generated by this aerodynamic element.
A great variety of different flap arrangements for varying the aerodynamic lift generated by an aerodynamic element of an aircraft are generally known. For example, there are many known configurations of high lift flaps arranged along the trailing edge of a main lifting wing of an aircraft. Such conventionally known flap arrangements are generally rather complicated, i.e. having a complex geometry and construction, and require a complex support and drive mechanism for selectively extending and retracting the flap arrangement. Such flap arrangements typically and generally aim to selectively smoothly increase or reduce the chord length, the curvature, and/or the angle of attack of the sectional aerodynamic profile of the respective aerodynamic element.
As an alternative, it is also generally known to rigidly fix a sheet metal plate or the like on the trailing edge of an aerodynamic lift-generating element so as to form a perpendicular wall protruding substantially perpendicularly into the transverse plane airflow. This will alter the pressure distribution over the aerodynamic element, and therewith alter the magnitude of the lift and the resistance generated by this aerodynamic element. Although this has been known as a theoretical and experimental concept, it has never been further developed into a practically useful arrangement for varying the aerodynamic lift generated by an aerodynamic element of an aircraft.
In view of the above, it is an object of the invention to provide a flap arrangement that enables a rapid adjustment or variation of the aerodynamic lift generated by an aerodynamic element of an aircraft, so as to enable a controlled load variation and lift distribution of the aerodynamic element of the aircraft within projected effective or working ranges. It is another object of the invention to provide a flap arrangement that is extremely simple in design, construction, and operation. It is a further object of the invention to provide such a flap arrangement that can selectively either increase or decrease the aerodynamic lift generated by an aerodynamic element, in comparison to the clean configuration of the aerodynamic element. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification. The attainment of these objects is, however, not a required limitation of the present invention.
The above objects have been achieved according to the invention in a flap arrangement provided on a trailing edge of an aerodynamic lift-generating element of an aircraft. The aerodynamic lift-generating element will also simply be called an aerodynamic element herein, and may particularly be a main lifting wing, an auxiliary or secondary wing, a flap, an aileron, a rudder, an elevator, a stabilizer element such as the horizontal and vertical stabilizers or tail plane and fin of an aircraft tail unit, or the like. Throughout this specification, the terms xe2x80x9cliftxe2x80x9d and xe2x80x9caerodynamic liftxe2x80x9d refer to the component of the aerodynamic force generated by the aerodynamic element in a direction perpendicular to the apparent air flow direction relative to the aerodynamic element. Thus, the general term xe2x80x9cliftxe2x80x9d is not limited to a vertically upward lift, but rather could also refer to a horizontally directed lateral aerodynamic lift, e.g. in the case of a rudder or the like.
According to the invention, a relatively small movable and controllable auxiliary flap is movably arranged at the trailing edge of an aerodynamic element in such a manner so that the auxiliary flap is selectively movable to any selected one of at least three positions. In a first end position, which is an upper end position in the case of a wing or the like as the aerodynamic element, the auxiliary flap protrudes into a first boundary layer of the airflow over a first surface of the aerodynamic element (i.e. into the upper boundary layer of the airflow along the upper surface of the wing). In a second end position (e.g. the lower end position in the case of a wing), the auxiliary flap protrudes into the second boundary layer of the airflow along the second surface of the aerodynamic element (e.g. the lower boundary layer of the airflow along the lower surface of the wing as the aerodynamic element). In a third neutral position, between the first and second end positions, the auxiliary flap does not protrude into and does not influence either of the two boundary layers.
The trailing edge of the aerodynamic element is preferably a flat planar trailing edge, rather than tapering to a single line edge at an intersection-of the two opposite aerodynamic surfaces of the aerodynamic element. Preferably further, the auxiliary flap has a configuration of a flat planar rectangular plate, i.e. without any aerodynamic airfoil shape, curvature, or thickness variation. Also, preferably, in at least the first and second positions, the auxiliary flap extends parallel to the flat planar trailing edge, and substantially perpendicular (e.g. 90xc2x0+10xc2x0) relative to a central chord line intersecting the trailing edge and extending between the first and second aerodynamic surfaces of the aerodynamic element. That also approximately corresponds to a substantially perpendicular protrusion of the auxiliary flap into the respective boundary layer in the respective end positions. In the third position, the auxiliary flap may remain parallel to the plane of the trailing edge, or may extend substantially parallel to or along (e.g. xc2x110xc2x0) the central chord line.
More specifically, in a first embodiment of the invention, the auxiliary flap is rotatably connected to the aerodynamic element, e.g. by rotational means, so that the auxiliary flap can be selectively rotated through approximately 180xc2x0 to rotatably move the auxiliary flap among the above described first, second and third positions. The term xe2x80x9crotatablexe2x80x9d does not require complete freedom to rotate through 360xc2x0, but rather also encompasses partial rotation or pivoting. In the first position, the auxiliary flap extends substantially perpendicularly to the chord line of the aerodynamic element, while in the second position the auxiliary flap extends substantially 180xc2x0 opposite from the first position, and in the third position, the auxiliary flap extends substantially parallel to the chord line of the aerodynamic element, i.e. respectively 90xc2x0 between the first and second positions. To achieve this, one of the longitudinally extending edges of the auxiliary flap is secured to a shaft that is rotatably supported and extends parallel to the trailing edge of the aerodynamic element in the direction of the span (e.g. the wing span) of the aerodynamic element. This shaft has a relatively small diameter, e.g. a diameter corresponding substantially to the thickness of the auxiliary flap.
Alternatively, instead of a shaft, a cylindrical drum or roll having a larger diameter can be rotatably supported and arranged along the trailing edge of the aerodynamic element. In this embodiment, the circular cross-section of the cylindrical drum is preferably at least partially received in a semi-cylindrical recess along the trailing edge of the aerodynamic element. The cross-sectional diameter of the drum is substantially greater than (e.g. 2, 3 or even 4 or more times) the cross-sectional thickness of the auxiliary flap, and may correspond to a dimension in the range of one quarter to one half of the height or thickness of the aerodynamic element at the trailing edge perpendicular to the chord line thereof.
The shaft or drum may additionally be slidable or shiftable in a direction along the planar trailing edge between the two opposite surfaces of the aerodynamic element. Thereby, the sliding or shifting of the shaft or drum can further accentuate the protrusion height of the auxiliary flap in the first and second positions achieved by rotation of the auxiliary flap about the axis of the shaft or drum.
Any conventionally known actuator and drive transmitting transmission mechanism, e.g. an arrangement of an electric motor, a hydraulic motor, a pneumatic motor, a pneumatic cylinder and/or a hydraulic cylinder, in combination with a gear drive, a toothed belt or gear belt drive, a worm gear drive, a shaft drive, a rack-and-pinion drive, or a crank drive can be connected to the shaft or drum for driving the movements thereof. The required actuation movements are controlled, e.g., by control signals provided by the aircraft""s flight control computer via electrical conductors or the like.
In a second embodiment of the invention, the auxiliary flap is slidingly mounted on the trailing edge of the aerodynamic element, e.g. by sliding means. Particularly, the opposite side edges of the auxiliary flap extending in a direction between the two opposite sides of the aerodynamic element are slidingly received in corresponding guide rails or tracks provided on the trailing edge of the aerodynamic element. The auxiliary flap is slidingly shiftable along the guide rails or tracks parallel to the planar trailing edge of the aerodynamic element in either direction toward the opposite boundary layers of the airflow along the opposite surfaces of the aerodynamic element. The guide rails or tracks advantageously extend entirely from the first or upper surface of the aerodynamic element to the second or lower surface of the aerodynamic element. The maximum sliding displacement of the auxiliary flap in one direction sets the flap into its first end position protruding into the first boundary layer, while the maximum sliding displacement in the opposite direction sets the flap into its second end position protruding into the second boundary layer, and an intermediate sliding position of the flap represents the third neutral position in which the flap does not protrude into either one of the two boundary layers. This sliding flap can be driven by any of the above described actuators and transmission arrangements, and preferably is driven by a rotary drive through an eccentric cam that engages the auxiliary flap so as to selectively slidingly drive the auxiliary flap.
According to further special features of the invention, a plurality of separately actuatable auxiliary flaps of the above described type can be arranged along the trailing edge of the aerodynamic element. With such an arrangement, the individual auxiliary flaps can be individually and independently actuated so as to either increase, decrease, or not influence the local aerodynamic lift generated by the local associated area or portion of the aerodynamic element, such as a wing. In this manner, the lift distribution and therewith the load distribution along the span of the wing can be easily varied or adjusted.
Further according to the invention, the above described auxiliary flap may be provided on the trailing edge of any conventional lift influencing flap, e.g. along the trailing edge of the landing flap of an aircraft wing. Thereby, the inventive auxiliary flap allows a further adjustment or tailoring of the lift generated by the wing and its main flap, even with the conventional flap selectively extended or retracted into various configurations. The inventive auxiliary flap thus allows a fine-tuning or rapid-tuning adjustment and local variation of the lift generation pattern, of which the overall or gross lift generation is predominantly predetermined by the setting of the main flap.